The field of the present invention is the art of pyrometallurgy, particularly processes for high temperature treatment of particulate material by subjection to the action of an electrical discharge arc.
The prior art concerned with such processes teaches that in order to achieve a complete and controlled changed in materials subjected to the action of electrical discharges, all such materials must pass through the zone of discharge and their time of residence in this zone must be of a certain controlled duration. In an effort to accomplish such control, use has been made of an arc spread into a fan-like shape, known as an expanded arc. Methods of obtaining and expanding an arc column were known before the Second World War and described by W. Weizel and R. Rompe in "Theorie Elektrischer Lichtbogen und Funken" (Leipzig, Barth, 1949), however such methods, although of scientific interest, do not lend themselves to industrial exploitation. The inevitably high thermal losses in the rotating cylinder and inability to inject sufficiently large quantities of feedstocks without affecting the stability of the discharge proved the main obstacles preventing industrial utilization of such devices.